1. Field of the Invention
This invention relates to a semiconductor device which includes a protective resistor and in an extended arrangement to a device for detecting magnetism including semiconductor elements, which are prevented from being destroyed by an applied high voltage owing to noise, or the like.
2. Description of the Related Art
A conventional device for detecting magnetism includes a substrate and mounted thereon a thin film type ferromagnetic magnetoresistive element essentially consisting of a ferromagnetic body. This conventional device detects changes of magnetism, for example as changes of an electric voltage, using the characteristic that a value of the resistance of the ferromagnetic magnetoresistive element is changed by applying magnetism (or a magnetic field) thereto.
When such ferromagnetic magnetoresistive elements are used as parts for an automobile, there is a possibility that a high voltage (for example, the noise from an ignition device or energy accumulated as a reactance component) will be applied to the device and will destroy the device, including a semiconductor element or the like, which processes signals from the ferromagnetic magnetoresistive element.
To solve such a problem, use has been made of another conventional device, a Zener diode, which has a large capacitance to absorb the high voltage. However, since a Zener diode is constructed as a discrete part and its size is very large, it is impossible to integrate it with other circuit parts. Therefore, to make an integrated circuit, usually a protective resistor for protection of the electric circuit is formed on an IC chip. However if the resistor is formed by diffusion, the size of the diffusion resistor must be considerably large since a diffusion resistor is easily broken down by large energy. Hence, the breakdown voltage of the PN junction thereof must be increased.
The technique of forming a polycrystalline silicon resistor on a silicon dioxide film as the protective resistor is also used in the prior art. However, there is a limitation for integration, because a polycrystalline silicon resistor is easily broken down by large energy, too. Furthermore, since a conventional device for detecting magnetism does not include a MOSFET using a polycrystalline silicon as a gate, but mainly includes a bipolar transistor as a circuit component of the circuit for processing the signals from the magnetoresistive element, there process of forming a polycrystalline silicon resistor must be added.